7 Tips to Make Sure Your Jam Sets Up | The Kitchn 7 Tips to Make Sure Your Jam Sets Up 7 Tips to Make Sure Your Jam Sets Up Email I am an equal opportunity jam eater. I am just as happy with the loose, sloshy batches as I am the ones that have a firmer consistency. I love to use the runny varieties to flavor plain yogurt or as a sweetener for green smoothies. The slightly overset batches are perfect for serving with cheese plates or as the filling in a thumbprint cookie. However, if your jams never quite hit the set mark and you’re getting frustrated, here are a few tips and tricks for getting a better final consistency. Understand pectin. Pectin is the fiber that holds up the cell walls of fruits and vegetables. It exists in all produce, but some things have more of it than others. High pectin fruits like blueberries, apples, and cranberries don’t need any additional pectin and can be used in combination with other fruits to boost their pectin.

If you’re working with low pectin fruit like strawberries or pears, there’s no shame in using some commercial pectin, as it will give the sugar more fiber with which to bond. Use a candy thermometer. When you’re making jam with traditional amounts of sugar, you’re aiming to cook it to 220°F. That’s the temperature at which sugar forms a gel and can bond with the pectin (whether it naturally occurring in the fruit or you’ve added it). Monitoring the temperature can give you confirmation that you’re on the right track. Watch the way the jam drips. Swirl your spatula through your cooking jam, hold it up over the pot, and watch how it falls. If the jam runs right off the spoon and looks thin and runny, it’s not done yet. However, if it forms thick droplets that hang heavily off the bowl of the utensil, but don’t immediately fall off, it is either nearing completion or is done. Use the freezer test. At the beginning of cooking, put two or three small plates or bowls in the freezer. As you begin to approach the end of cooking, pull one out and put a small dollop of jam into the middle of the dish.

Tuck it back into the freezer for two or three minutes (take your jam off the heat during this time, because if it the test tells you it’s done, you will have just spent three minutes overcooking your jam). When the time is up, pull the dish out of the freezer and gently nudge the dollop of jam with the tip of your finger. If it has formed a skin on top that wrinkles a bit when pushed, it is done. If it is still quite liquid and your finger runs right through it, it’s not done yet. Watch and listen. I realize it might sound a little zen-like, but I’ve gotten to the point where I truly believe that most batches of jam will tell you when they’re done. I find that the cooking noise takes on a frenzied quality that sounds more like a sizzle than a gentle boil. The look of the boil also changes towards the end. Foam subsides, jam starts to gather more thickly on the sides of the pot, and it begins to splatter more violently. Use a low or no sugar pectin.

One of the reasons that people often wind up with runny jam is that they couldn’t bear to use the amount of sugar necessary to get a conventionally sweetened batch to set. If you’re trying to lower your sugar consumption but still want jam, try Pomona’s Pectin. It allows you to make a spreadable jam that’s sweetened with a small amount of sugar, honey, Stevia or other alternative sweetener. Give it time. Jam can take up to a week to achieve its finished set. Don’t declare it a failure ten minutes out of the canner. Patience pays. Visit Marisa online & check out her Making Jam - Preserving Preserving An introduction to making your own jam Making Jam preserving | fruits | grow your own | recipes Making jam is the ideal way to preserve the taste and nutritional value of summer fruits so that they can be enjoyed throughout the year. It also ensures that a glut of produce will not go to waste or become boring! Many people use pectin (a plant derived powder) as a setting agent, however it is possible to make wonderful well set jams using just sugar and fruit since the fruit itself contains pectin.

Making Jam If you have never made jam before, you will be surprised at how simple it is. The most important thing to remember is that the pan, spoon, and jars used must be scrupulously clean to prevent bacteria from getting into the jam and spoiling it. Making jam with 1 - 2kg of fruit at a time is ideal - more than that and it is difficult to get the jam to set because it cannot be boiled fast enough. 2kg of fruit is enough to fill 6 standard sized 450g jam jars. Ideally fruit should be used as soon as possible after picking - and some not quite ripe fruit should be included in the mix since it contains a higher level of pectin which will help the jam to set. The fruit should be crushed (how much depends on the desired texture) and simmered in a pan for around half an hour. While simmering pectin will be drawn out of the fruit. Next add an equal weight of caster sugar * to the weight of the fruit - i.e. 1kg of sugar to 1kg of fruit - and heat the mixture gently until all of the sugar has dissolved.

If the sugar is heated in the oven before use it will dissolve into the fruit juices much faster. Test if the sugar has all dissolved by dipping a spoon into the mixture so its back is coated and check there are no sugar crystals visible. The raise the temperature so the mixture boils rapidly, stirring occassionally to prevent the jam sticking to the bottom of the pan. * Different fruits require a different ratio of fruit to sugar. Check out recipes online for the fruit(s) you plan to use. One thing to note is that sugar hardens fruit. Therefore, if you are making jam from soft fruits such as strawberries, you should mix the fruit with sugar and heat them together from the start. This will help prevent the fruit from disintegrating when heated. Any froth/scum which accumulates on the surface of the mixture can be skimmed off carefully while boiling. It is important not to overcook the jam, therefore you have to check regularly to see if the jam is ready to set. Put a teaspoon of the jam onto a (fridge cooled) plate and let it cool down for 30 seconds to a minute. If it remains as a runny liquid, it is not ready to set and so you need to continue heating.

If however it has thickened with a skin on top, and it wrinkles when pushed with the spoon or a finger, then it is ready to set. Turn off the heat and leave the jam to cool for around 15 minutes without stirring. This will start the setting process and also prevent any solid fruit from floating up to the top of the jar when it is decanted. Pour the finished jam into sterilised hot dry jam jars using a sterilised funnel and immediately cover the surface of the jam with waxed paper discs (for example, grease proof paper) and seal with a sterilised lid or cellophane. When the jars are completely cool stick on a label with a description of the contents and the date made. If the jam does not set in the jars, then pour it back into the pan and boil it up again, this time with the juice of a small lemon. Jam Recipes Different fruits have different levels of pectin and therefore will set differently. Fruits such as blackcurrants, redcurrants, gooseberries, and cooking apples have high levels of pectin and so will set will. Fruits such as strawberries, cherries, and blackberries have low levels of pectin and so will not set too well.

Therefore, it is common to mix fruits with high pectin with fruits with low pectin in order to make delicious well set jams. Sterilising Equipment To sterilise the jars, funnel and spoons before use, wash them on the hottest dishwasher setting (or in very hot soapy water), rinse with boiling water from the kettle, and drain them thoroughly on a clean tea towel. Alternatively wash well in soapy water and place the jam jars in a cool over (130 degrees C) for around 20 minutes. This will dry the jars as well as sterilising them. Storing Jam Jam should be stored in a cool, dry, dark location. If it is steamy or damp - for example, in a kitchen - the moist atmosphere can cause mould to form on the surface of the jam. If mould should form on the surface, you can simply discard the top 1/2 to 1 inch of jam since the rest of the jam will still be good to eat. A waxed disc dipped in brandy or other alcohol will prevent mould from returning. Jam should be eaten within one year so you will be ready to make a new batch the following summer!

Shopping List Making jam Making jam Published by Sarah Horrocks Published on 19 January 2009 Jam on your morning toast or afternoon scone is a comfort and a treat, and when you can say your blueberry jam is home made it's an added source of pride! Making your very own jam and jelly is really easy; here are our tips, golden rules and recipes to get you started. Check out our jam recipes! Equipment The list can be long, but you use most of these utensils everyday. - A stainless steel bowl for the jam (copper spreads heat better but is not advised for soaking) - A slotted spoon and a metal ladle (plastic doesn’t resist heat well) - Large glass jars - A big wooden spoon to stir the fruit (prolonged contact with metal can cause oxidation) - Kitchen scales (the quantities of fruit and sugar need to be exact) Make sure you equip yourself with a blender if you want to make jelly. Sugar Calorie-free jam simply doesn't exist, and sugar is vital (it preserves the fruit). The less sugar you use the shorter the time you can keep your jam, which is why jam must contain at least 60% sugar.

Among the types available, the best to use is granulated sugar (cane or beet), light brown cane sugar (more fragrant) or special jam sugar that contains pectin to help it set better. Setting and thickening agents To avoid runny jam or jelly you need to use a setting agent. The most common is pectin, a natural substance found in some fruits. Sugar for jam already contains it so extra isn't required. If you use light brown sugar or ordinary white sugar you can buy the pectin in pastry aisles in supermarkets or in pharmacies. Another possibility which is more tedious is to make the pectin yourself, by boiling apple or orange peel. the latest setting agent at the moment is agar agar, which is very effective and ideal for saving runny jam. Use 1 to 2g powdered agar agar per kilo of fruit. Bear in mind that agar agar must be used cold then heated and it sets when it cools. You must first make your jam, let it cool, add the agar-agar, then heat it up let it simmer for 3-4 mins before finally putting it in a jar. Remember to add lemon juice during cooking for prettier colours and a firmer texture.

If you get runny jam, add the juice of two lemons and re-heat everything for 5 mins. Your jam or jelly should be saved. Cooking jam Contrary to the persistent myth, jam does not have to be cooked for hours: most of the time 30 mins is long enough. Stir your jam throughout the cooking process to stop it sticking, but there’s no need to skim it constantly. Skim once and repeat if you think necessary. Precautions, sterilisation, preservation and labelling Fruit is fragile even once cooked, so impeccable sterilisation is essential. Wash your utensils carefully, wash your jars and boil them for 5-10 mins. We advise screw on lids with a joint that dilates with heat to keep air out. Used covers are less effective than new ones. If your jam is correctly sterilised you can keep it for several years, but it is best used in the first 6 months of making it (after which it loses its flavour). Keep your jars in a cupboard away from light and damp. Label your jars with the date and flavour (it's not always easy to tell your strawberry from your raspberry !). Once opened, keep in the fridge.

You know your jam is edible if there are no signs of mould and you get the characteristic ‘pop’ when you open the jar that tells you it has stayed airtight. Tips, flavours and decoration ideas Today's culinary trends are for mixing flavours, so add aromatic herbs and spices such as rosemary or thyme to apricot , mint and bee balm to strawberry, ginger and cinnamon to citrus fruit and vanilla to melon or chestnut jam. Also delicious are dried fruit, walnuts, hazelnuts, almonds, figs, apricots etc. Finally, flowers and vegetables have made their way into the jam aisles too, and you'll find rose petal, bay, violet and hibiscus jelly as well as tomato, carrot and pumpkin jam, onion chutney...anything is possible!

Decoration and presentation - For a retro effect decorate your jars with Vichy fabric and ribbon - Pop a cinnamon stick or a star anise into your jars - Place a rosemary stem or whole flower petals in your jelly - Citrus jams and jelly are prettier with citrus peel added The science and magic of jam-making | Andy Connelly | Science | The Guardian Food alchemy The science and magic of jam-making Commercial jams are the sickly sweet sisters of homemade jam, but a grasp of the science will help you get yours just right Getting the pectin content of your jam right makes the difference between a semi-rigid, elastic 'gel' and sloppy fruit sauce. Photograph: R White/Corbis Food alchemy The science and magic of jam-making Commercial jams are the sickly sweet sisters of homemade jam, but a grasp of the science will help you get yours just right Thursday 3 October 2013 07.30 EDT First published on Thursday 3 October 2013 07.30 EDT Close The rule is, jam tomorrow and jam yesterday – but never jam today.

Lewis Carroll Jam-making conjures up images of domestic idylls, an escape to the mountains to live on your wits, and jam. The seemingly simple mixture of fruit and sugar held together by a web of pectin strands can be both beautiful and maddening. A jam worthy of a Women's Institute rosette , however, might have a nature so tender that it quivers when cut with a spoon to reveal sparkling, ruby-like faces. This sweet treat was named late, in the early 1700s, but "jam" captures the difference between it and the (in my opinion) inferior jelly. Jellies are made from homogeneous fruit juice with none of the wonderful texture-giving "crushed" fruit. Jam as we know it only seems to have emerged in the 19th century. It took a cheap and reliable source of sugar from the West Indies to make jams affordable. Before this, sugar was considered a spice and the price in Europe was such that only the richest could afford it. Preserves made from sugar were too precious to spread thickly on toast. Instead they were eaten as "spoon sweets" with feasts being capped off with the distribution of delicate silver spoons laden with fruit preserves.

You may still be offered such treats with a glass of cooling water in the Middle East and eastern Europe. The first European sugar preserves made use of that seemingly magical substance, honey. The earliest fruit preserves would be made by mixing fruit pulp with honey and allowing it to dry in the sun, creating a texture more like that of a jellied sweet. The high-pectin quince lent itself to making this well-set fruit preserve. In Greece, a common spiced preserve of quinces was known as melomeli (apple honey) and was thought to be an aphrodisiac and to aid digestion. In Britain, it was adapted to incorporate other fruits, such as pears, damsons, plums, and finally Seville oranges, becoming marmalade. Eventually, when sugar prices fell late in the 17th century, marmalade became a soft jelly that, smeared on toast, became a staple of the Scottish breakfast. Jam only reached the masses in the 1880s when it was used to enliven the dark wholemeal bread eaten by the working classes. Many of these factory-produced jams contained more sugar and colour than fruit.

The quality of commercial jams have improved greatly since then but they are still the sickly sweet sisters of a good homemade jam. And besides, buying jam gives no way near the satisfaction of making it yourself. The recipe Jam recipes mostly comprise equal weights of fruit and sugar. You can play with this 1:1 ratio as much as you want, but too much fruit and you may lose the preserving effects of the sugar; too much sugar and it may crystallise during storage. The choice of fruit for jam-making is almost endless. I always try to use seasonal fruit to get the best flavour for my jam. Slightly unripe or "just ripe" fruit will form a jam more easily than very ripe fruit as it contains more pectin and is more acidic. 1kg fruit 1kg granulated sugar Lemon juice and/or pectin (depending on the fruit you use) Start by removing any leaves and twigs, wash the fruit if you feel it necessary, and remove any stones. Add the fruit to a pan big enough to ensure the fruit does not reach more than halfway up the side. Heating Place your pan on a low heat. As the fruit heats through, a glorious fresh, warm smell will fill the air.

Prolong this by heating slowly until a very gentle boil is reached. Cook until tender – any longer and the fruit will lose its shape. No sugar is added at this stage because a high sugar concentration can cause water to be removed through osmosis and result in hard, unappetising fruit. You might need to add a little water though if your fruit is very dry. Boiling is key to jam-making because it releases a long fibrous compound known as pectin. Even though pectin only makes up 0.5-1% of the jam, you will have to learn to play it like a snake charmer or you will add your tears to your mixture. The first handling of a jam the morning after making is full of trepidation. The jam maker's nightmare is to find a wet, sloppy strawberry sauce, not the semi-rigid, elastic substance that chemists describe as a "gel": a liquid dispersed in a solid. Pectin forms the solid that holds the liquid together. Some fruits, including apples, blackberries and grapes, can do this alone as they contain sufficient pectin.

Some fruits are low in pectin , however, and so need a little more help, for example apricots, rhubarb and strawberries. You can add commercial pectin, which is extracted from the white inner skin (the pith or "albedo") of citrus fruits or from apples. You can also buy special jam sugars with added pectin. But jam makers of yore discovered through trial and error that if they mixed low-pectin fruits with high-pectin fruit (often apple) they could create the perfect consistency. Personally, I like to mix high and low pectin fruits to keep it "in the garden", for example I might add a cooking apple to my blackberry jam. Pectin was first isolated by French chemist Henri Braconnot in 1825 and was named from the Greek pektikos, which means congealed or curdled. It is a polysaccharide so, like cellulose and starch, it is made up of long chains of sugar molecules. In fruit, pectin is concentrated in the skins and cores where it acts as structural "cement" in the plant cell walls.

In jam, pectin forms a mesh that traps the sugary liquid and cradles suspended pieces of fruit. Branches that stick out from the long chains of pectin bond with each other to form the three dimensional network that jam makers crave. In a solution, these branches are reluctant to bond, first because they attract water molecules, which stops them bonding, and second because they have a slight negative electrical charge, which means they repel one another. To solve the first problem we add sugar, which binds to the water molecules and frees up the pectin chains to form their network. The negative charges are reduced by acid naturally found in the fruit or added to the mixture. The acid reduces the electrical charge on the pectin branches and so allows them to bond. To increase acidity lemon juice can be added. But be careful: if your mixture is too acidic, this will damage the pectin. As a rough guide, the juice of a whole lemon (30-40ml) will be needed for very low acid fruit, whereas half a lemon will be enough for medium acid fruit, and you won't need any for the high acid fruits.

In general, fruit with high pectin will also have high acidity and vice versa. Adding the sugar Add the sugar and stand back as it starts to foam up the sides of the pan. A sentimentality-inducing childhood smell of sweet fruit fills the air. Allow the sugar to dissolve over a low heat then bring rapidly to the boil. Avoid stirring at this point as you may break up the fruit or cause crystallisation. A foamy scum may form on the surface of the jam; this is normal and can be removed by adding a little butter (about 20g) to break the surface tension or by skimming it off with a spoon while your mixture is cooling. This is the exciting bit: the smell of jam fills the air and you're desperate to get it into jars and on to some toast, but patience is required. However, you will normally have to wait around 5–20 minutes for the pectin network to form. The time varies depending on the type of fruit, the type of pan etc. A wide-mouthed pan is ideal as it allows water to escape, helping to bring our precious pectin molecules closer together.

Time to pour There are many ways of telling when your pectin network has formed and you are ready to pour the jam out. It normally forms at around 104-105C, when the sugar content is high enough to allow the pectin branches to join. Unfortunately, temperature is not a reliable signal because it varies according to acidity, amount of pectin, etc. My preferred method is direct measurement. Pour a little blob of jam on to a cooled saucer, let the jam cool in the fridge and then push against the side of it with your finger. If the surface wrinkles it means the pectin network has solidified, setting point has been reached, and you should take the mixture off the heat. If you don't boil it long enough the pectin network will not form properly. Boil it too long you risk not only losing the fresh flavour and colour of the jam but having a jam with the texture of set honey. Cooling and decanting into jars This is my favourite part, but I allow the jam to cool and thicken for about 10 minutes before pouring it into jars, to prevent the fruit from floating to the top.

Try not to leave the jam too long, however, as lukewarm jam is a great breeding ground for mildew spores which are present in the air. To keep you busy while you are waiting, get your pre-sterilised jars ready. You will need five or six of them. My preferred method of sterilisation is to wash them in soap and hot water, rinse them with clean water to remove any detergent, and dry them in the oven at about 160C. Jams can remind us of summers past, even summers several years gone. It is the sugar and acid that makes this possible. Jams usually contain about 60% sugar, which is enough to stop most microorganisms growing. The high acidity also makes it an unpleasant place to breed. However, some moulds can grow even in these harsh conditions and so it is important to take care when preparing and sterilising your jars. The satisfying gurgle of jam being poured is music to the ears. Each jar should be topped up to just less than a centimetre below the surface. Capping and storage I remember being puzzled why my parents always put a waxed paper disc on the surface of their homemade jam.

I now know that it prevents the condensation of water on the jam's surface. Condensed water would dissolve sugar, producing an area of low sugar concentration and allowing mould growth. I must confess that jam never sits in my cupboard long enough to worry about this. Now that our jam-making is at an end, there is only one stage to go: eating. I always struggle not to get overexcited and try my jam straight away before it has developed its "quiver". I am torn; I feel I should wait until the autumn, when I can close my eyes and relive summer. But I'm realistic. I wait till the next day to spread the noble jam thickly on a delicious chunk of simple bread and butter. Food texture Home → - Video Items - → Gelling agents, thickeners & stabilisers The texture of food is important for the look and feel of food, and also for digestion. Thickening and stabilising agents are gums that work with emulsifiers to maintain the texture of food, and create texture in water-based products that would otherwise be runny. Ingredients such as flour, cornflour and arrowroot have been used for thickening sauces for centuries.

In jam, pectin is used to thicken the fruit juices. Pectin is naturally present in fruit, but many fruits don’t contain enough to make the jam set so extra is added. Natural sources predominate – many thickeners are derived from plants and seaweeds. Others are made by the chemical modification of natural cellulose, and some, such as xanthan gum, are even made by fermentation. Thickeners and stabilisers tend to be both odourless and tasteless. The gums are polysaccharides – polymers made up of sugar molecules. The majority of these polysaccharides have few or no calories, but many function as fibre in the digestive system. This eases bowel function, and some are used as bulk laxatives. Most of these gums can form gels at room temperature, and (rather like non-drip paint) they lose their thickness when they are stirred. This makes mixing easier during the production process as they become runny, and then when the mixing stops, they thicken up again.

Some of the most important thickeners and stabilisers are: Agars (E406) are partly sulfated polysaccharides that were first discovered in Japan in the 17th century which are extracted from two different species of red algae. They have a very high gel strength, and when dissolved in water the gelation process is reversible at 85°C. They are used in jellies, bakery products, sauces, fillings and meat products. Alginates (E400-404) are salts of alginic acid, a viscous gum formed by the cell walls of brown algae. Food uses include thickening fruit drinks, soups and sauces, and as a gelling agent in jellies and bakery fillings. They are also an important component of several indigestion remedies. Carrageenans (E407) are sulfated polysaccharides extracted from several species of red seaweed. They are used to thicken dairy products such as ice cream and milk shakes and water-based jellies. They are also components of various processed meat products.

Gum Arabic (E414) is made from the sap of the acacia tree and is a mixture of saccharides and glycoproteins (proteins with attached sugar molecules). Commercially, most is extracted from trees in countries south of the Sahara desert in Africa, and the biggest producers are Chad, Nigeria and Sudan. Food uses include hard jelly sweets and soft drinks. Guar gum (E412) is extracted from guar beans, which predominantly grow in India. It is a type of water-soluble polysaccharide called a galactomannan, where the polymer chain is made up of galactose sugar units, with mannose sugars attached to it. Uses include baked goods and bakery fillings, thickening dairy products like yoghurt and milk, and as a stabiliser in sauces and dressings. It is also used in meat products. Locust bean gum (E410), also known as carob bean gum, is (like guar gum) a galactomannan polysaccharide, and is extracted from the seeds of the carob tree.

It is water soluble, and is used as a thickener and stabiliser in a variety of products, including sauces, salad dressings, fruit fillings and ice creams. Pectin (E440) is a gelling agent that is usually extracted from dried citrus peel or the solids that remain when the juice is pressed from apples. It is a polysaccharide made by plant cell walls, and as well as being used to help jams and jellies to set, it is used as a stabiliser in milk drinks and fruit juices. Sodium carboxymethyl cellulose (E466), or sodium CMC, is a water-soluble semi-synthetic thickener, made by reacting cellulose with an acetic acid derivative. It is used in a variety of products such as breads and cakes, ice creams, and milk and fruit drinks. Starch (E1401–1451), in its various forms, is one of the most common thickeners in food products. These polysaccharides are isolated from a number of different crops, including wheat, corn, rice, potatoes and cassava. Numerous starch derivatives are also available where the properties have been chemically modified.

Unlike many other gums, they are not water-soluble, but the molecules do enter their lattice-like structures, and so they thicken up when mixed with water. Many different types of foods contain starch ingredients, from sauces and pie fillings to sweets and puddings. Xanthan gum (E415) is made by the fermentation of glucose or sucrose with the microorganism Xanthomonas campestris. It is commonly found in sauces and salad dressings, where it acts as a stabiliser and helps prevent the emulsion from separating. Processing | Food Technology & Processing Food Technology & Processing Processing Introduction This section will address the various methods used to preserve food products. Included will be a description of various heating processes as well as preserving methods using cold temperatures. The detail on each category will depend on its popularity. Foods Preserved By Heat Retorted-pressure process It is possible to destroy bacterial cells and spores by exposure to heat for various lengths of time. The severity of the process depends on the pH of the food. Table 1 lists various foods and their respective pH value. Foods that have a pH exceeding 4.6 (low acid) must be processed under pressure in order to reach “commercial sterility”.

Which is the condition achieved by application of heat which renders such food free of viable forms of microorganisms of public health significance, as well as any microorganisms of non-health significance capable of reproducing in food under normal storage conditions. The canning of low-acid foods requires a large capital investment therefore further detail is not necessary for this publication. Acid/Acidified Foods Acid foods have a natural pH of 4.6 or less such as tomatoes. Because of the natural acidity these products can be cooked at atmospheric temperatures (212°F.) or less, usually around 190°F., and filled hot for preservation. Many fruits and their juices are processed in this manner. Sometimes acids or acids foods are added to low acid foods to yield products that have a final equilibrium pH of 4.6 or less: These foods are called acidified and have a specific regulation in the Code of Federal Regulations (CFR), see page 127. Many products that new processors are trying to produce fall in this category. Relishes, most hot sauces and many pickled products are termed acidified foods. Strict regulations have been set up for these products; see part 114 CFR under regulations.

Foods Preserved by Cold Refrigerated This method of preservation is growing in popularity. It involves blending and/or processing of foods and then chilling them to temperatures just above the freezing point of water, approximately 32-36°F. The growth of most microorganisms is retarded at these temperatures and many may be killed. There are however, certain microorganisms that are able to grow slowly and the spores do survive. Any abuse in holding temperatures upwards of 38°F. may cause spoilage problems and decreased shelf-life. Certain organisms capable of causing food-borne illness may also become a problem. Freezing This is probably one of the safest forms of food preservation. Frozen food is normally held at O°F. The freezing and storage process kills most bacteria, but the spores are able to survive. Once frozen foods are thawed they should be utilized promptly. The equipment for freezing foods can be quite costly and the energy to operate it is also expensive. Small scale operations are in existence, but usually most freezing operations require a high capital investment. Foods Preserved by Reducing Moisture Drying Bacteria, yeasts and molds are like people, in that they must have moisture to survive.

Dehydrated and freeze-dried foods have a low moisture level and therefore are shelf stable at room temperature. Moisture is removed in dehydrated foods by hot air, whereas freeze-dried products are produced under a vacuum with minimal heat involved. Reducing Water Activity Water activity (aw) is probably a new term for most people. It is essentially a measure of free or available water in a food system. It is the equilibrium relative humidity of food divided by 100. Pure water has an aw of 1.0. Most foods will be at .97 to .99, but dissolved substances such as sugar and salt will lower this reading by binding the moisture. Other substances which can reduce water activity include: starches; phosphates; polyhydric alcohols such as sorbitol; mamitol; propylene glycol and glycerol. Dried foods have an aw of 0.60 or less. Bacteria need more water than most yeasts and molds. The osmophilic yeasts can grow where there is very little moisture available. Table 2 illustrates the minimum water activity of certain types of microorganisms. High sugar and acid are the two main preserving factors for jams and jellies.

Certain cheese based dips are also preserved by lowering the aw and controlling pH. Jams, Jellies & Related Products Jellies, jams and preserves are popular items with many specialty food processors. Producing a quality product that jells properly is not always easy. Sometimes one ends up with ice cream topping instead of jelly. The four essential ingredients for proper jelly manufacture are fruit, pectin, acid and sugar. These ingredients must be present in proper quantities to yield an acceptable jellied product. Some fruits, such as apples, have enough natural pectin to make a high quality product. Others require added pectin especially if they are used for making jelly; which has to firm. Most processors prefer adding pectin to all formulations so that they can use fully ripe fruits; reduce cooking time; and increase yields. Sugar concentration and pH are two very critical factors in jelly manufacture. Normally a pH of 3.1 with a sugar content of 67.5 % is considered optimum. There are several excellent references on jelly manufacture including, “Handbook for the Fruit Processing Industry” from Hercules, Inc. and A Complete Course in Canning, listed under references.

Other Methods of Preservations Aseptic This process involves sterilizing food at high temperature for a short time, cooling it in a sterile chamber and then packaging the product in a sterile container under aseptic conditions. This system has historically only been used on high acid products. However, there are certain low-acid products being produced today. The equipment is expensive and technological expertise is a must for aseptic processing. Irradiation The use of ionizing radiation has been cleared for use on raw fruits, raw vegetables, spices and raw pork. This is a cold process with little heat involved. It will extend shelf-life of the above named products. Consumer acceptance and the high cost of an irradiation facility will delay the use of irradiation in our food system. Preservatives Preservatives of various types have been used for many years. Smoking and salt were two of the earliest substances used. There are many others in use today. Preservatives can be divided into two categories according to function; (1) those which act to control or prevent growth of microbes, and (2) the ones used to control deteriorative chemical reactions such as rancidity.

Salts of various acids such a propionic, sorbic, and benzoic are some of the most important microbe inhibitors used in foods. Calcium propionate is added to, bread and other baked products to retard mold growth. Potassium sorbate also is effective against mold as well as yeasts in cheeses, syrups, soft drinks, jams, mayonnaise and pickles. Sodium benzoate is an especially effective preservative against yeasts and bacteria in high acid foods such as sauces and fruit drinks. It is also popular for use in carbonated beverages. Table 3 gives the use levels of the various preservatives. Parabens are yet another category of preservatives that are active against yeasts and molds. The methyl and propyl parabens antimicrobial effectiveness is best at a pH of 7 or above. Sulfur dioxide has been used as a sanitizing agent in wine-making since ancient times. Today sulfur dioxide and its sulfite salts are useful in controlling microbial growth and maintaining color in a wide range of food products.

Sulfur dioxide and the sodium and potassium forms of sulfite, bisulfite and meta bisulfite are all considered GRAS (Generally Recognized As Safe) for use in foods except fresh fruit and vegetables (other than potatoes) although their status is under active review by FDA. Sulfiting agents are effective antimicrobials preservers of quality, including color and flavor, however, their safety has come under close scrutiny. This is due to adverse reactions experienced by certain asthmatics, including several deaths. It is estimated that about 8% of the asthmatic population is sensitive to these substances. If you use a sulfiting agent, include it in the ingredient statement. Properties and use limits of some commonly used preservatives are listed in Table 7. Table 7. Properties and Use Limits of Commonly Used Preservatives. Agent

Question: What agent is normally used to make jam set?
Answer: Pectin